The 2008 Physical Activity Guidelines for Americans recommended 150 to 300 minutes of moderate-intensity or 75 to 150 minutes of vigorous-intensity aerobic activity weekly for optimal health. However, these guidelines acknowledged uncertainty on the upper threshold of benefit or potential harms of high activity levels.  Using data from 6 pooled cohorts from the National Cancer Institute Cohort Consortium (baseline 1992-2003) with self-reports of leisure-time physical activity (LTPA), Arem and colleagues aimed to address this question. The total cohort consisted of 661,137 men and women with a median age of 62 years and a median follow-up of 14.2 years in which 116,686 deaths were accrued. When compared to subjects with no reported LTPA, individuals exercising less than the recommended minimum of 7.5metabolic-equivalent hours per week exhibited a 20% mortality benefit (HR 0.80 [95% CI 0.78-0.82]), individuals exercising 1 to 2 times the recommended minimum exhibited a 31% mortality benefit (HR 0.69 [95%CI 0.67-0.70]), and individuals exercising 2 to 3 times the minimum experienced a 37% mortality benefit (HR 0.63 [95%CI 0.62-0.65]). Researchers observed a ceiling of mortality benefit at the threshold of 3 to 5 times the minimum suggested LTPA (HR 0.61 [95%CI 0.59-0.62]). Additionally, there was no evidence of harm associated with exercise at a level of 10 times or more than the recommended minimum (HR 0.69 [95%CI 0.59-0.78]). Similar dose-response and threshold effects were seen for cardiovascular and cancer mortality.

Conclusion: Achieving the minimum levels of physical activity recommended in the 2008 Physical Activity Guidelines was associated with a mortality benefit.  Increasing health benefits were observed with increasing levels of physical activity up to 5 times the minimum recommended activity level and no harm was associated with higher levels of physical activity.  These findings support physical activity as cornerstone of optimal health and reduce concerns for potential harm associated with high levels of physical activity.

Summarized by Jehu S. Mathew and Steven M. Bradley

•  Arem H, Moore SC, Patel A, Hartge P, Berrington de Gonzalez A, Visvanathan K, Campbell PT, Freedman M, Weiderpass E, Adami HO, Linet MS, Lee IM, Matthews CE. Leisure time physical activity and mortality: A detailed pooled analysis of the dose-response relationship. JAMA Internal Med. 2015 Apr 6.